Energy storage devices have been recognized as having the potential to decrease the energy consumption in a host of mobile and stationary applications. In land vehicles, for example, energy storage devices can be used as part of a regenerative braking system in order to capture and subsequently reuse vehicle kinetic energy which would otherwise be dissipated as heat in the vehicle brakes each time the vehicle decelerates. Energy storage devices cannot only reclaim vehicle kinetic energy during deceleration or braking and therefore reduce energy or fuel consumption of a given vehicle with a given primemover, they can further permit downsizing of primemovers to a more energy or fuel efficient size since horsepower for acceleration, passing, and/or hill-climbing can, for the most part, be provided by the energy storage device.
Many automotive regenerative braking devices have been proposed with little or no success. The devices have been inefficient, bulky, heavy, and/or not readily controllable. For example, regenerative braking devices using flywheels or pressurized fluid have been inefficient, i.e., the round-trip energy transfer efficiency of these devices has been relatively low. Devices using resilient means, such as metal springs, have been bulky and/or heavy; further, the driving and braking torques of such devices have not been readily controllable.
The copending U.S. Patent Applications mentioned in the above Cross-Reference all disclose regenerative braking devices employing elastomers for storing energy. The elastomer may be in the form of elastomeric rods. To store energy, one end of each rod is rotated relative to the other end, thereby torsionally stressing the rod about its longitudinal axis. In laboratory tests of elastomeric rods, plotting torque versus the number of rotational turns of one end of a rod relative to its other end, the torque increased with increasing relative rotation until the rod buckled and then began to form knots similar to the knots formed by rubber bands in model airplanes. When the rods buckled, the torque dipped and then continued to increase at a lesser rate. This lesser rate of torque increasing is advantageous in that greater amounts of energy may be stored in the elastomer at lower torque levels. However, the knotting causes the rods to abrade. The abrasion did not manifest itself as an excessive friction loss but did cause tears to develop in the elastomer, thereby severely reducing the fatigue life of the elastomer.